Dental professionals, for a number of different dental procedures, use powered dental handpieces containing a rotating head for receiving a dental tool. Preferably, the handpiece is constructed with an ergonomically friendly shape to reduce the user's stress level associated with gripping the handpiece for extended periods of time. Gears attached to rotatable shafts disposed inside the handpiece mesh with each other to rotatably drive the dental tool from a driving source associated with the handpiece.
As shown in FIG. 1, a typical ergonomic handpiece 10 includes a body 20 having a first portion 21 extending to a head 27 that is disposed at an angle of 21 degrees with a second portion 25. A drive train 15 disposed inside body 20 must therefore conform to the spatial constraints of the angled inner walls of the handpiece body, as shown in FIG. 1. A housing 23 rotatably carries a drive gear 22 about an axis 24 that is rotatably driven by a source (not shown). Drive gear 22 meshes with a gear 28 at one end of a shaft 26 that includes a gear 30 at the opposite end of shaft 26. Shaft 26 is configured to rotate about an axis 31. Gear 30 meshes with a gear 34 disposed at one end of shaft 32 that includes a gear 36 at the opposite end of shaft 32. Shaft 32 is configured to rotate about an axis 38. Gear 36 meshes with gear 42 at one end of shaft 40 that includes a collet 44 at the opposite end of a shaft 40 for securing a dental tool therein. Shaft 40 is configured to rotate about an axis 46. Thus, in response to the drive source, drive gear 22 and shafts 26, 32, 40 are urged into rotational movement about respective axes 24, 31, 38, 46 so that a dental tool mounted in collet 44 is rotatably carried about axis 46.
Axes 24, 31, 38, 46 of drive train 15 are disposed in coplanar alignment. Coplanar is defined herein to indicate that axes 24, 31, 38, 46 are each coincident with a single, vertically disposed plane. As shown in FIG. 1, at least one axis of axes 24, 31, 38, 46 is also nonparallel with the other coplanar axes, resulting in the drive train 15 having substantial cost and performance disadvantages. By virtue of the ergonomically friendly angle formed between body portions 21, 25, axes 24, 31, 38 that extend only through portions of body 20 are not parallel to each other. As shown in FIG. 1, axes 31, 38 are not parallel to each other. Because gears 30, 34 rotating about respective axes 31, 38 mesh, at least one, if not both, of gears 30, 34 are tapered. Tapered gears are more expensive to produce, since special methods of manufacture are required. Alternately, it may be possible to substitute face gears in place of tapered gears, but face gears also suffer from the same disadvantages as tapered gears. Additionally, the nonparallel arrangement of drive gear 22 and axes 24, 26, 38 are especially sensitive to mounting distances and angle errors and tend to produce a higher amount of noise during operation, especially when either tapered or face gears are used.
What is needed is a drive train for an ergonomic dental handpiece that does not require either a tapered or face gear for gears disposed adjacent to the junction between the first and second portions of the handpiece.